The preparation by a sol-gel process of dense, alumina-based ceramic abrasive grain is described, for example, in Leitheiser et al, U.S. Pat. No. 4,314,827, assigned to the assignee of the present application. This patent teaches making abrasive grains by employing chemical ceramic technology by gelling alumina monohydrate with a precursor of at least one modifying component followed by dehydration and firing. The modifying component is selected from zirconia, hafnia, a combination of zirconia and hafnia, and a spinel derived from alumina and at least one oxide of cobalt, nickel, zinc, or magnesium.
Abrasive products containing ceramic abrasive grits made by a sol gel process have been found to perform in a superior manner as compared to the best fused synthetic abrasive mineral in many applications. A typical example of a high performance fused synthetic abrasive mineral is formed of fused alumina-zirconia available, for example, under the trade designation "NorZon" from the Norton Company.
Other references which disclose the preparation of alumina-based ceramic abrasive grains include the following:
Cottringer et al, U.S. Pat. No. 4,623,364, issued Nov. 18, 1986, entitled Abrasive Material and Method For Preparing The Same.
Gerk, U.S. Pat. No. 4,574,003, issued Mar. 4, 1986, entitled Process For Improved Densification of SolGel Produced Alumina-Based Ceramics.
Amero, U.S. Pat. No. 3,450,515 discloses a method of making impregnated sintered bauxite abrasive grains. The grains are prepared by impregnating sized particles of calcined bauxite with an aqueous solution of manganese, iron or copper ions, and firing the impregnated particles for at least two hours at 1600.degree. C. The resultant abrasive grains are said to contain agglomerated alpha alumina crystals of a size between 50 and 200 microns, with the preferred crystal size of about 100 microns and higher being preferred. Bauxite is an impure form of alumina containing other oxides including, for example, iron oxide, titania, and silica. Instead of producing abrasive grains of higher strength, the resultant grains are said to be weaker, a result which the patentee appears to desire for stainless steel snagging.
References which disclose the preparation of ceramics include the following:
Church et al, U.S. Pat. No. 4,007,020 discloses a method of producing a refractory abrasive body by forming a porous skeletal body which is impregnated with a compound of a metal capable of being converted to an oxide in situ at relatively low temperatures, heating the body so impregnated at a temperature well below the normal vitrification to a temperature of at least 600.degree. F. and for a time sufficient to convert the compound impregnated therein to an oxide and repeating the impregnation and heating steps until the desired degree of hardness is obtained. The porous body can be made from relatively finely divided materials which may be relatively pure powders, mixtures of powders, or impure powders, including additives in the form of discrete particles, fibers, fillers and the like. The powders are molded and bound together or bound together and molded with a binder which may comprise the impregnating compound or other suitable binder prior to treatment. Such refractory materials include alumina, beryllia, magnesia, titania, and zirconia.
Berneberg et al., U.S. Pat. No. 4,552,786, discloses a method for densification ceramic materials which involves dissolving a ceramic precursor in a supercritical fluid, infiltrating the low density ceramic material with the ceramic precursor-laden fluid, and reducing the solubility of the ceramic precursor in the fluid to impregnate the ceramic precursor in the void spaces of the ceramic material.
Bailey et al., U.S. Pat. No. 3,859,399 discloses a method for making dense composite ceramic bodies of titanium diboride, boron carbide, silicon carbide and silicon. The ceramic bodies are produced by forming a mixture of titanium diboride, boron carbide and a temporary binder into a desired shape to obtain a coherent green body which is siliconized by heating in contact with silicon to a temperature about the melting point of silicon, where upon the molten silicon infiltrates the body and reacts with some of the boron carbide therein to produce silicon carbide in situ.
Bugosh, U.S. Pat. No. 3,108,888, discloses processes for producing colloidal, anisodiametric transition aluminas by heating colloidal, anisodiametric boehmite at a temperature in the range of 300.degree. to 1000.degree. C. until the desired conversion has occurred, and is further directed to the process for making strong, shaped bodies by forming a mass of such boehmite particles and so heating until the boehmite is converted into a transition alumina, and optionally to the alpha form. The temperature of heating could be above the sintering point. Another method involves the introduction of grain-growth inhibitors and/or sintering-promoting substances such as iron oxide, manganese oxide, copper oxide and titanium oxide to impregnate a porous object of gamma alumina derived from fibrous colloidal boehmite alumina powder. Impregnation by aqueous solutions of soluble precursors of the desired oxide modifier are suggested, followed by drying to fix the modifier on the surface of the individual gamma alumina powders. This patent does not, however, teach the preparation of abrasive grits by this method.